Measuring instrument



Jan. 7, 1941. c. s. MOORE MEASURING INSTRUMENT Filed Dec. 14, 1939 2 Sheets-Sheet 1 INVENTOR COLEMAN B. MOORE BYW ATTO R N EYS Jan 7, 1941. c, '5, MOORE I MEASURING INSTRUMENT Filed Dec. 14, 1939 2 Sheets-Sheet 2 INVENTOR IULEMfiN B0 MO'LTDRE ATTORNEYS \IIIIIIIII" Patented Jan. 7, 1941 UNITED STATES PATENT OFFICE MEASURING INSTRUMENT Application December 14, 1939, Serial No. 309,270

10 Claims. The present invention relates to self-balancing potentiometers and more particularly to a mechanical relay mechanism whereby the potentiometer circuit may be rebalanced. in-response to unbalance thereof and a pen moved across a chart to a position proportional to the value of a condition being measured.

It is an object of the invention to provide a simple relay mechanism to convert the deflections of a measuring element into proportional movements of an adjusting member.

It is a further object of my invention to provide a mechanism for rebalancing a potentiometer in response to unbalancethereof in exact accordance with the amount of unbalance in a simple and (efficient manner.

It is a further object of my invention to provide a relay mechanism for a potentiometer whose sensitivity may be adjusted while the instrument is operating without in any way interfering with the operation of the mechanism thereof.

The various features of novelty which characterize my invention are pointed out with particularity in the claimsannexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and specific objects obtained with its use, reference should behad to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

In the drawings:

Fig. 1 is a front view of my potentiometer mechanism with various parts broken away and other 5 parts omitted for the sake of clearness;

Fig. 2 is a front view of the galvanometer clamping and detecting mechanism;

Fig. 3 is a side view taken from the right of Fig. 2;

40 Fig. 4 is a view of the right-hand side plate and.

parts mounted thereon;

Fig. 5 is an enlarged view of the pawlmechanlsm; and

Fig. 6 is a wiring diagram of a potentiometer 45 circuit.

Referring now to the drawings of which a detailed description will be made, there igshown a gaivanometer which is connected in potentiometric circuit with a thermocouple and a slidewlre.

Potentiometric circuits of the type contemplated herein are well known, such, for example, as disclosed in the Harrison Patent 1,898,124, and include, as is shown diagrammatically in Fig. '6,

- 5d a known source of voltage I impressed acrossa resistor 2, commonly termed the instrument slidewire, the galvanometer 3 and source of variable voltage, such as a thermocouple 4, being connected in series to oppose the known voltage across a variable portion of said resistor '2. The por- 5 ti'on of the resistor 2 in circuit is determined by the position of a contact 5 along the slide-wire, the slide-wire and contact being relatively movable. When the val able voltage, for a given adjustment of the slide-wire, is equal and opposite 10 to the known voltage, the galvanometer is in its null position, but on an increase above or decrease below the known voltage of the unknown voltage, the galvanometer will be deflectedin one direction or the other respectively proportionately to the Iii magnitude of the increase or decrease. This inventionis concerned with the means by which deflections of said galvanometer control slidewire adjustments to continuously rebalance the potentiometer system, and move an indicator 20 which may take the form ,of a pen to make a record of the changes in the value of the condition. The elements of the potentiometer circuit along with the rebalancing and. recording mechanism are conveniently located in a casing 6 having a 25 door I that is provided with a window 8 through which various of the elements of the mechanism may be viewed. The galvanometer clamping mechanism is located in a separate housing 9' within the case 6 to protect it from dust and undesirable fumes that may enter the case when the door is opened for the purpose of changing the chart or making necessary adjustments. Also located within the casing are a pair of side plates in and II which serve to support mechanism to be later described.

A pointer l 2 (Figs. 2 and 3) of the galvanometer 3 is periodically clampedbetween a stationary abutment l3 and a movable abutment l4 that is vertically under [3 and forms part of a lever I5, 40 pivoted at l6 and biased in a clockwise direction by spring IT. The lever i5 is periodically given counter-clockwise movements around its axis to free the pointer l2 so that the latter may assume a position dependent upon the circuit unbalance. These periodic movements are given by means of engagement between a spring member i8 attached to the lower portion of the lever i5 and a pin lain the end of a lever 20 that is attached to and moves with a shaft 2 l As the lever 20 moves in a counter-clockwise direction, prior to the time pin I9 engages the spring l8, the lower edge of the lever will engage a pin 22 in the end of an arm of bell-crank 23 that is pivoted at 24. The second armof the bell-crank 23 actsQthrough a pin ,25on lever 26, I to move a lever 21, pivoted at '28, in a counterclockwise direction. A ,fee1e'r 29, that is adapted to engage the galvanometer pointer l2 and measure its position; is moved away from the pointer to permit the latter to assume a new position, by the counter-clockwise movement of lever 21. This is accomplished by means of a bent over arm 30 on the lever 21 that engages an arm 3| on the feeler to move the latter around its pivot 32 against the tension of spring 33.

By the time arm 29 has moved pin 22 sufficiently to shift feeler 29 completely out of the path of deflection of pointer l2 the pin l9 will engage spring l9 to move the abutment l4 downwardly enough to free the pointer so that it can assume its new position. The force which moved lever 29 counter-clockwise is then removed and the parts return under the action of springs l1 and 33. On their return movement the lever l5 under force of the spring |.1 acts to clamp the pointer between abutments l3 and I4.

Movement of feeler 29 and levers 21, 23 and 20 continues under the action of spring 33 until the feeler 29 engages the pointer I2, at which point they are stopped. The lever 20 is then in a position corresponding to the position of the pointer l2.

In order to change the sensitivity of this feeler mechanism or the ultimate position of lever 20 for a given position of the pointer l2 it is only necessary to shift the position of pin 25with respect to the point at which it engages levers 23 and 21. If pin 25 is moved downwardly movement of bell-crank 23 is decreased with respect to movement of lever 21 and vice versa. This adjustment is valuable since it permits the instrument to be adjusted for galvanometers of V various sensitivities and for slight variations in the voltages curves of difierent thermocouples. This adjustment may be made easily and accurately while the instrument is in operation without disturbing any of the operating parts by merely rotating a screw member 34 that extends through the front of the mechanism housing 9. The screw is in threaded engagement with a stationary support 35 and has its right end acting against a bent over arm 36 on a lever 31 that is pivoted at 38 and biased in a clockwise direction by a spring 39. This lever has a stud shaft 49 on its outer end that acts as a movable pivot pointfor the lever 26 supporting pin 25. As the screw 34 is moved toward the' right the pin 25 will be lowered to change the amount of movement imparted to bell-crank 23 for a given movement of the lever 21.

The manner in which shaft 2| is given its counterclockwise movements and the manner in which the clockwise movements thereof are used to control the action of the relay mechanism will now be described with reference to Fig. 4.

Extending through the side plate II is a shaft 4| that is driven at some suitable constant speed by a motor, not shown. This shaft has two cams 42 and 43 attached to it the former of which engages a roller on one arm 44a of a multiple armed lever 44 tooscillate this lever around its pivot 45; Oscillating motion is imparted to the shaft 2|, which extends through the housing 9 and side plate II, by means of the engagement between a projection 46 on an arm 41 attached to the shaft and an arm 44b of the lever 44. As'the cam 42 rotates arm 41* is. first moved counter-clockwise to rotate the shaft 2| in a. direction to move feeler 29 away from the pointer I2 and to unclamp the pointer. Continued rotation of the cam will then permit the shaft to rotate clockwise under the bias of spring 33, as previously described, until feeler engagement between a projection 50 thereon and a brake member 5|. This brake is periodically released just before the arm 41 starts its upward excursion and is reapplied after arm 46 has reached its highest position. A pin 52 extends from the side of the brake to limit the downward movement of the secondary pointer.

The brake 5| is applied and released in timed relation to the movement of arm 41 by means of a pin 53 on a pawl actuating lever 54 that is moved around its pivot 55 by the cam 43.

As the lever moves clockwise it returns a pair of driving pawls 58 and 59 to their starting position in addition to releasing brake 5| just prior to the end of its stroke. Upon counterclockwise movement of lever 54 the brake 5| is w first applied to secondary pointer 48 and then the driving pawls are started on their work stroke which is terminated when roller 51 reaches the low portion of cam 43.

The driving pawls on their work stroke are adapted to engage one of the teeth in a large gear wheel 65 that is attached to a shaft 5|. The point along the work stroke at which the pawls engage the gear determines the amount of rotation that is imparted thereto and the pawl that engages the gear determines its direction of rotation. Pawl 58 rotates gear 60 clockwise and pawl 59 rotates it counter-clockwise.

The pawl 55 is pivoted at 62 on a pawl carrying arm 53 that is journaled on shaft 6|. The

pawl normally has a gravity bias around its pivot 52 in a clockwise direction and is limited in movement by a pin 54 on the arm 53. The outer end of arm 63 is connected by a link to an arm on lever 54. The second pawl 59 is 55 pivoted at 55 to a second pawl carrying arm 61, also ioumaled on shaft 6|. The pawl 59 has a gravity bias counter-clockwise to a position limited by a pin 58 on the arm 51. The outer end of arm'S'fi is connected by a link 69 to a second so arm on lever 54.

This arrangement'is such that as the lever 54, moves counter-clockwise under the bias of spring 59 the pawls will be moved by their supporting arms around shaft M as a center. Normally 06 with the gear to rotate it an amount depend- 7 ing upon the position of pin 49. This is accomplished by having a lever 10 pivoted at 1| to the arm 53. This lever has a lower curved and 10a, is provided with an opening 12 that surrounds the point at which the link 55 is at- 16 tached to arm 63 and has a pin 19 at its upper end that is adapted to force pawl 58 toward gear 66. In a like manner a lever II is pivoted at 15 to arm 61. This lever isprovided with d a lower curved end "Ila, has an opening 16 that surrounds pivot 66 and has. a pin 11 adapted to force thetooth of pawl 59 into engagement with gear wheel 69.

The operation of the mechanism so far dem scribed is as follows. The parts are shown in Fig. 4 in the position they will assume just after brake has been released and before secondary pointer 49 has dropped against pin 52. Rotation of the cam 42 in a, clockwise directionwill then M move lever ll so that arm 41 can rise under the bias of spring 33 until the feeler 29 is stopped by engagement with pointer l2. During this time the projection 46 on arm 41, which also underlies secondary pointer 48, has lifted 48 to a at position corresponding to that of pointer 12. At

this time the radius of cam 43 decreases sufficiently for the brake ii to be applied to part I it of the secondary pointer to hold the latter in m place. Cam 4! now quickly permits the lever 43 W to rotate clockwise under the blas of spring It to move arm 4'! to its lowest position. This, by means of shaft 2| and lever 20, moves the feeler it away from the pointer and causes abutment it to be lowered to permit the pointer it to swing 3W tree. At the same time that lever M is turning clockwise. cam 43 is permitting the lever lit to move counter-clockwise under the bias of spring lit. This movement, through links 6% and W c and through arms 63 and 61. carries the pawls it ti and it around the edge or gear W. n the galvanometcr pointer was in its neutral position the pin it will be in the position shown and no movement will be imparted to the gear. It, now ever, the pointer was deflected, for example, to rm the left of its mid-position in Fig. Q the pin M .will be located above its position of Fig. i and'will be in the path oi? end Ma oi lever it. Therefore, when arm t'l has moved sufliciently for its to engage it, the lever M will pivot around 115 causttt ing pin ii to force the tooth or pawl b9 into engagement with a tooth of gear 60. For the rest of the movement of arm 6'! the pawl 59 will rotate gear 6W. It will be obvlous'that the further displaced the pointer 12 is from its midtid position, the sooner in the cycle pawl 59 will begin rotating gear 60. For a deflection of the pointer it to the right of its mid-position in Fig. 2 the pin 49 will be moved to a position in which. it will be engaged by arm Illa. This, by means of tin pin 13, will force pawl 58 into engagement with gearfill to rotate that gear clockwise an amount depending upon the amount of deflection of pointer H from its midpoint. If the secondary pointer 48 was not in its mid-position it will be m iorced back to that position on each cycle by either arm a or Ha engaging pin 49. The brake M is weak enough to permit this action to take place.

As has been described above the gear 60 is ca periodically rotated an amount proportional to the deflection of the galvanometer. This rotation is used to move the contact 5 along the slidewire 2 and to shift a pen along a chart in order to make a record of the value of the condition it being measured.

The slide-wire 2, in the instrument, takes the form of a coil of wire that is helically wrapped around a core I9 which is supported on a suitable portion of the instrument. Journaled in it this core is a shaft 80 that has on its lower end a bracket 8| that extends around the core and up the outside thereof in proximity to the slidewire. The contact 5 is carried by this bracket and as the shaft 80 is rotated the contact travels around the slide-wire following a helical path 6 from the top to the bottom thereof to bring more or less resistance into the galvanometer circuit. Shaft 80' is rotated by means of a gear 82 on its upper end that meshes with another gear 83 that is on the shaft Bl to which the gear 69 is at- 10 tached. Therefore, as gear 60 is rotated the contact 5 will be shifted along the slide-wire 2 to rebalance or tend to rebalance the potentiometer circuit.

A chart 84 to receive a record of the value of the condition being measured is mounted in the instrument and is moved past a pen 85 at a suitable rate by means of a chart drive roll 86 that is journaled in the side plates i0 and H. This roll is prr' 'ided with a knob 81 by which it may be rotated by hand, but is normally driven through a ratchet and gear mechanism 88 driven intermittently from an arm Me of the lever M.

The pen 85 is mounted in a carriage 89 that is in threaded engagement with a helically threaded lid shaft 9% journaled in the side plates it and ii. The shaft 90 is rotatedby means of a gear M on its outer end which meshes with the gear til. Therefore, as the gear til rotates the shaft M will be rotated to move the pen across the chart to a w position corresponding to the value of the condition being measured.

While in accordance with the provisions of the statutes, 1 have illustrated and described the best form of my invention now known to me, it willbe dd apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of my invention as set forth in the appended claims, and

that in some cases certain features of my inven m tion may sometimes be used to advantage without a corresponding use of other features.

Having now described my invention. what I claim as new and desire to secure by Letters Patent is: M

l. in a measuring instrument, the combination of an element movable in response to variations in the value of a measurable condition, means to measure the position of said element, a member set in accordance therewith, a driven memberja w pair of drive members each adapted to drive said driven member in a given direction, means to move said driving members through a path nor- I mally out of contact with said driven member and means operated by said member to cause {in engagement between one of said drive members and said driven member depending upon the position of the member.

2. In a measuring instrument, the combination with an element deflectable in accordance with Gil variations in the value of a measurable condition, means to measure the position of said member comprising a first lever moved through a path into a position determined by the position. of said element, a second lever moved by said first lever, apparatus operated in accordance with the position assumed by said second lever, and means to vary the position of said second lever with respect to a given position of said first lever H comprising a thrust connection between the two levers and means to shift said thrust connection 9 while said levers are in operation.

3. In a measuring instrument, the combination of an element movable in response to variations in a measurable condition comprising a first lever said element in position, a feeler periodically moved from a predetermined point through a path in which it will be stopped by said element, mechanism to be operated in accordance with the position in which said element is engaged by said feeler and a sensitivity adjustment for said mechanism operable to change the relation between said feeler and mechanism while they are in motion.

5. In a measuring instrument, an element deflectable in response to variations in the value of a measurable condition, a lever positioned in accordance with the position oi. said element, a

secondary element periodically moved by said lever, means to maintain said secondary element in position, a driven member, a pair of driving members, means to move said driving members through a path adjacent said driven member, and means operated by said secondary element to move one of said driving members into driving relation with said driven member.

6. In a measuring instrument, a driven member, a pair of driving members, pivoted supports for said driving members, means to move said supports and driving members through a path adjacent said driven member, a lever carried by each support to move its driving member into driving relation with said driven member, an element positioned in accordance with the value of a measurable condition on either side of a neutral position and when on either side of said neutral position being in the path of one of said levers, whereby as one of said levers engages said element its driving member will be moved into position to drive said driven member.

7. In a measuring instrument, a driven member, a pair of driving members normally out of engagement with said driven member, means to move said driving members through a circular path in opposite directions around said driven member, means moved with each of said driving members adapted to move the latter into driving relation with said drivenmember, an element deflectable to a position determined by the value of a condition, a secondary element positioned by said element in the path of said means moving with said driving members to obstruct the movement of the same and cause one of said driving members to drive said driven member.

8. In a measuring instrument, an element positioned in accordance with the value of a condi-' tion, a secondary element positioned by said element, a driven member, apair of driving members movable in opposite directions through paths adjacent said driven member, means operated in accordance with the position of said secondary element to move one of said driving members into driving engagement with said driven member and means to adjust the relation of said secondary element with respect to said element while said members are operating to change the point at which the driving member will be moved into engagement with said driven member for a given position of saidelement.

9. In a measuring instrument, an element movable to a position corresponding to the value of a measurable condition, a feeler biased toward a position determined by the position of said element, an arm moved by said feeler in its biased direction, means to move said am and feeler in the opposite direction to predetermined positions, a secondary element, means to hold said secondary element in an adjusted position, means acting in timed relation with the means to move said'arm to release said holding means and permit said secondary element to move to a predetermined position, and means on said arm to reposition said secondary element as said feeler and arm are moved in their biased direction.

10. In a measuring instrument, an element defiectable in accordance with the value of a measurable condition, a feeler periodically moved 

